I would work at developing my "observer" self, the part of us that realizes that even though we don't know the person well, it still hurts to have them "reject" us. Everyone pretty much feels that way I think, wants to be liked? When the pain of being rejected gets to me, my observer self points out the discrepancies of having not known that person well or how I didn't particularly like that person either but just wanted to be liked, etc. and that takes some of the sting from the rejection for me and I go "do something else" for a bit and it's not so bad.

Use the feeling, since you can identify it so well, to "play" with? Hone your skills of telling who you like better/worse or who "really" likes you and who doesn't, etc. If you can get a bit of "separateness" by doing your own thing, the rejections get to be a bit less personal, often more expected and even funny sometimes since you'll learn to expect them from people more shallow than you so when they finally occur it will be a "win" for your skills of discriminating who's a good person to follow-up for friend and who was only pretending or has other issues you don't want to get caught up in anyway. It's a way of getting to know yourself more as SeptemberMorn says and concentrating on yourself, takes the power out of "their" hands and puts it where it belongs in your own.